The application of sleeve labels on containers filled with pourable food products is known in the field of labelling.
The above said sleeve labels are obtained by:                cutting a plurality of flat rectangular or square labels from a tape which is unwound from a reel;        overlapping, by folding, the opposite vertical edges of each cut label so as to form a respective sleeve label; and        welding the opposite edges of each label.        
Patent application WO-A-018806, in the name of the same Applicant, discloses, for example, labelling machines, in which each sleeve label is first formed on a respective sleeve drum, and then transferred on a relative container, for example by inserting the latter within the corresponding sleeve label.
The above said labelling machines of the known type substantially comprise:                a carousel rotatable about a first axis arranged, in use, vertically; and        a plurality of carrying units for respective containers, arranged along a circumferential edge of the carousel and rotated about the first axis of the carousel along a labelling path.        
Each carrying unit is also fed with a relative container to be labelled at an inlet station of the labelling path and provides the relative container on which the sleeve label has been applied at an outlet station of the labelling path.
Proceeding from the inlet station to the outlet station along the labelling path, each carrying unit is also fed with a relative flat label, forms a relative sleeve label and applies this sleeve label to the relative container.
Each carrying unit also comprises a lower support element adapted to support a lower wall of the relative container and an upper retaining device adapted to cooperate with an upper portion of the relative container to retain it in a vertical position during the rotation of the carousel about the first vertical axis.
Each support element comprises, in turn:                a tubular upright, which is fixed to a horizontal plane rotatable of the carousel; and        the cylindrical sleeve drum, which engages the relative tubular upright in a rotatable and axially sliding manner with respect to a second axis.        
In particular, the sleeve drum supports a relative container on its upper surface.
Each sleeve drum is also mobile under the control of a cam, between:                a totally lowered position reached at the inlet and outlet station of the conveying path; and        a lifted position reached between the inlet and the outlet stations of the conveying path.        
Each sleeve drum also comprises a pneumatic driving device formed by a vacuum source and a plurality of suction holes arranged on its side surface and connectable selectively with the vacuum source.
In the totally lowered position, the sleeve drum is substantially contained within the upright to allow the container to enter or exit on/from the carousel.
In the lifted position, each sleeve drum projects from an upper surface of the relative support element and is adapted to receive a respective flat label on its side surface.
The sleeve drum also rotates about its second axis to allow the flat label to be completely wound about the sleeve drum until it reaches a tubular configuration, in which the opposite vertical edges thereof overlap.
More precisely, during the winding of the label, the driving device is actuated so as to retain the label on the side surface of the sleeve drum in virtue of the action of vacuum.
Each carrying unit finally comprises a welding bar adapted to longitudinally weld the overlapped edges of the relative sleeve label.
Once the welding of the overlapped edges of the sleeve label is completed, the driving device is switched off and the sleeve drum is returned to the lowered position within the upright.
Accordingly, the sleeve label is released from the side surface of the sleeve drum, is retained above the upright by an upper annular edge of the upright, and finally is slidingly engaged by the relative container.
At the outlet of the carousel, the containers are fed in a substantially vertical position by a conveying device through a heating device adapted to shrink the labels about the bottles.
Since the sleeve labels are fed through the heating device always in contact with a resting plane defined by the above mentioned conveying device, the known labelling machines of the above disclosed type have some drawbacks mainly resulting from the fact that such machines do not allow to selectively control the position of the sleeve labels along the relative containers and therefore have a relatively low flexibility.
A similar solution is also known from WO2010/040397 in the name of the same Applicant.
In order to selectively control the position of the sleeve labels along the relative containers, the same Applicant has proposed in patent application PCT/IB2011/055591 a labelling machine comprising:                a carousel of the above disclosed type, which provides containers with the relative sleeve labels in a first position; and        an additional module fed by the carousel and adapted to displace the sleeve labels in a second position with respect to the relative container.        
More precisely, the module comprises:                a further carousel rotatable about a third axis;        a plurality of further carrying units for respective containers arranged along a circumferential edge of the further carousel and rotated about the third axis by the further carousel; and        a plurality of transfer devices arranged along a circumferential edge of the further carousel, associated with respective carrying units and adapted to displace respective sleeve labels along relative fourth axes parallel to the third axis with respect to the corresponding containers.        
In greater detail, each further carrying unit comprises: a plate adapted to support the lower wall of the relative container, and a retaining element mobile between a lifted position in which it allow the entry and exit of the container on/from the module and a lowered position in which it cooperates with an upper portion of the relative container.
Each transfer device is mobile in parallel to the respective fourth axis and comprises a surface provided with a plurality of holes connectable to a vacuum source to retain the relative sleeve label and move the latter from the respective first to the respective second position.
The need is felt in the field to selectively control the position of the sleeve labels along the relative containers with a labelling machine as simple as possible.
Furthermore, the sleeve labels still have not been subjected to any thermal retraction when they are transferred from the carousel to the module, in the solution shown in patent application PCT/IB2011/055591.
Therefore, the labels have not yet been stably fixed to the relative containers when they reach the module.
Therefore, the solution shown in patent application PCT/IB2011/055591 does not allow to control the angular position of each sleeve label with respect to its axis, i.e. to ensure a predetermined angular orientation with respect to an axis of the container.
The need is therefore felt in the field to apply the sleeve labels on the respective containers in a desired angular position.
EP-547754 discloses a labelling machine, in which containers to be labelled are inserted within respective sleeve labels.
More precisely, as the containers move, respective sleeve labels are at first retained in a given position and then move together with respective containers.
DE-A-19716079 discloses a labelling machine, in which the sleeve labels move towards respective containers and are inserted onto respective containers at respective given prescribed positions.
More precisely, the labelling machine comprises a plurality of grippers which both move the respective labels relative to corresponding containers and apply those respective labels onto corresponding containers at respective prescribed positions.